The Role of EQA
Quality Assurance (QA)
QA is essential in clinical laboratories for the provision of precise and accurate analyses to support optimal patient care. QA improves test reliability through helping to minimise the variability, arising from biological or analytical sources, inherent in all quantitative measurements or qualitative examinations. An important contribution to the reliability of the results lies in ensuring correct specimen collection, handling and identification, which is particularly critical for microbiological and cytological examinations, but is also important for blood grouping and related tests. Though many modern analytical systems are apparently simple to use, the quality of results does not come automatically with the equipment and appropriate quality assurance and analytical quality control measures need to be taken, including staff motivation, training and assessment.
Overall, QA seeks to guarantee the right result from the right test, at the right time, on the right specimen from the right patient, interpreted using the right reference data. QA encompasses all measures taken to ensure the reliability of investigations, starting from test selection, through obtaining a satisfactory sample from the right patient, analysing it and recording the result promptly and correctly, to appropriate interpretation and reporting to the appropriate clinician for action, with all procedures being documented for reference.
Laboratories undertake two separate but complementary QA activities:
Internal quality control (IQC) assesses, in real time, whether the performance of an individual laboratory or testing site is sufficiently similar to their previous performance for results to be used; it controls reproducibility or precision, and facilitates continuity of patient care over time. Most IQC procedures employ analysis of a control material and compare the result with predetermined limits of acceptability - unsatisfactory sets of results may thereby be suppressed.
External quality assessment (EQA). EQA by contrast looks at differences between different sites testing the same analyte, so there can be continuity of testing over geography. This usually involves the analysis of identical specimens at many laboratories, and the comparison of results with those of other sites and a 'correct' answer; the process is necessarily retrospective.
All laboratories should apply QA procedures as part of maintaining professional standards of service, though requirements may differ according to circumstances and clinical application. To ensure continuity of patient care both within and between institutions, results and interpretations from laboratories should be interchangeable. The overriding need is for comparability of results, which requires good IQC practices and the complementary discipline of EQA.
General QA measures are essential in providing a secure basis within which this analytical quality control can be effective. In addition to the aspects mentioned above, any testing site
- must employ validated, reliable (reagents and instrumentation) carried out by
- trained, competent, motivated staff, on
- correctly collected and identified specimens, in
- an environment which is safe, clean, well-lit and appropriate to the task, and
- provide results which are recorded and interpreted correctly
Effective internal quality control procedures must be in place, and for quantitative determinations, sophisticated and statistically validated QC procedures have been evolved. The appropriate use of these techniques, including participation in all relevant EQA schemes, within a Quality Management System is a prerequisite for, and should be confirmed by laboratory accreditation.
The Place of External Quality Assessment
While IQC controls the precision of investigations, EQA should be providing an assessment of their accuracy (lack of bias) with respect to other test sites. This is done periodically and retrospectively, hence use of the term 'assessment' rather than 'control'. Though individual laboratory performance is frequently the main consideration, EQA also provides assessment of:
- the overall standard of performance (state of the art)
- the relative performance of analytical procedures (method principle, reagents, instruments)
- the specimens distributed
These are important in that EQA can provide information, through pilot surveys and schemes, on whether between-laboratory concordance is satisfactory and whether establishing a regular EQA scheme is likely to help stimulate any improvement needed. Similarly EQA may indicate analytical procedures showing excellent performance characteristics and which can be recommended, and also identify unsatisfactory procedures which should be discouraged. The assessment of materials provides a continuing check on the reliability of the scheme and its specimens, and most UK NEQASs use this as a real time quality assurance procedure before assessing participants' performance on any distribution.
Experience has indicated a number of fundamental criteria required for effective EQAS design, though it is important to remember that EQA can only document the need for, stimulate and monitor improvement: the improvements themselves come from effective quality assurance and IQC procedures within the individual participating laboratories. These criteria are:
sufficient recent data, achieved through:
- frequent distributions
- rapid feedback of initial performance information following analysis
effective communication of performance data, through:
- structured, informative and intelligible reports
- a cumulative scoring system
an appropriate basis for assessment, including:
- stable, homogeneous specimens which, where practicable, resemble clinical specimens
- reliable target values
Though the evidence is necessarily circumstantial, schemes satisfying these criteria are associated with improved between-laboratory comparability, both overall and in individual participating laboratories. Full and regular participation in appropriate external quality assessment schemes is therefore established as a necessary and integral part of the rational provision of a reliable clinical laboratory services.